"Sovereign debt sustainability is quintessentially a political issue," said Subbarao. "How much debt a government should raise is a political issue and, once the central banks become mindful of that, there is a risk that not only they might fail, but they might be crossing the line of being apolitical."

Central banks across the globe, including the European Central Bank, are being tested on their independence with them being forced to step in to save sovereign governments such as Greece and Portugal by indirectly supporting the fiscal profligacy.